The emergence of digital television broadcasting systems requires a change in traditional methods of communication and management, both between central distribution sites and remote stations and between remote stations and clients. Since data will be broadcast along with video and audio, aspects of the new systems will concern how data is reliably distributed among these entities, and how that data is stored. Since the television viewing environment is significantly different from other environments for the dissemination of data (such as the Internet), the architecture used for broadcasting data utilized in interactive applications must differ correspondingly. Specifically, accommodation must be made for late tuners (i.e., viewers who tune to a channel after a data downloading opportunity has elapsed), frequent channel changing, and the rapid speed of changing scenes during a television program, in contrast with the viewers' alacrity in responding to on-screen prompts which are related to those scenes.
Methods for broadcast distribution of data objects are known in the art. U.S. Pat. No. 5,613,065 describes a system for information broadcasting utilizing error check codes to determine if a remote client has received a broadcast without error. U.S. Pat. No. 4,908,828 describes the use of cyclic retransmission and CRC testing of a packetized broadcast. U.S. Pat. No. 5,631,907 utilizes cyclic transmission, block numbering and forward error correction for broadcast file distribution along with point-to-point communications to a particular station if blocks are not received after the last cycle. All of these methods require periodic retransmission of the data objects to ensure reliable reception, at a cost of increased bandwidth.
U.S. Pat. Nos. 5,222,061 and 5,535,229 describe systems that utilize retransmission of incorrectly received packets based upon individual requests by the client. These systems operate in point-to-point mode and do not take advantage of the broadcast nature existing for a digital television broadcast system. U.S. Pat. No. 5,619,689 adds the capability of aggregating retransmission requests through hub servers, but operates in a point-to-point message-acknowledgement system.
U.S. Pat. No. 4,868,866 describes a method for broadcasting database updates where the updates are modified by comparing the updated material to a record of what had been previously transmitted. This method requires that the central distribution site be aware of the state of data objects at each receiving client.
U.S. Pat. No. 5,666,293 describes a method of downloading software through a broadcast channel, where cyclic transmission of packetized data is used for reliable reception. In this method, the same content is broadcast to all clients and the client is responsible for deciding which data to download.
What is needed is a system for the distribution of content which is added to and associated with a TV program, or program segment, which makes the content available even to viewers who tune in after the program or segment has begun. It is therefore an object of the invention to provide such a system.
Another object of the invention is to provide a system that, in addition to providing a basic access window for viewers to receive content associated with a TV program, provides a mechanism for viewers to obtain the associated content after the basic access window has expired, using re-broadcasts.
Yet another object of the invention is to provide a system which allows for the retransmission of content to late requesters, which retransmission is performed in a bandwidth-conserving manner.
Still another object of the invention is to provide a system which allows for an on-request narrowcast if one or more users requests content after it is no longer efficient to rebroadcast the content.